Just when we thought it couldn’t get worse, Donald Trump has crossed another line, and it has nothing to do with misogyny and sexual assault. He has moved from nascent demagogue and proto-fascist, to a full-blown enemy of constitutional democracy. He now tells his supporters that the “system is rigged,” and if he loses it means the election will have been “stolen.” This is an explicit and unprecedented repudiation of our democracy and its institutions. He now states that his goal is to demolish the entire political establishment (“replacing a failed and corrupt establishment . . . with a new government”). He admits “our campaign represents a true existential threat like they haven’t seen before.” He threatens, like the worst sort of banana-republic dictator, to jail his opponent upon acquiring power, regardless of her exoneration by established due process. I cannot see how he could possibly take the Presidential oath to “preserve, protect and defend the Constitution of the United States." Like all fascist demagogues, he rejects our laws and institutions, and offers in their place “I alone.”

Up until now, many good people were unable to perceive the real Donald Trump, blinded by their long-time dislike of Hillary and allegiance to the GOP. But the real Donald Trump has now come into focus. As he announced three days ago on Twitter: “It is so nice that the shackles have been taken off me and I can now fight for America the way I want to.” I take this statement at face value. The sexual assault video and subsequent allegations finally have freed him from the need to make even a feeble attempt to deal with substantive issues or advance a coherent program. Mr. Trump is now back in his comfort zone, ranting against imagined enemies, spewing unfiltered vitriol, and wallowing in the adulation of rally crowds. His declared enemies now include his own party, pollsters, the financial industry, and the entire journalism profession. Yesterday’s speech was particularly unhinged, with eerie echoes of the 1930s: “Hillary Clinton meets in secret with international banks to plot the destruction of U.S. sovereignty.” He tells us now that without him we are lost: “This is a struggle for the survival of our nation, believe me. And this will be our last chance to save it on November 8, remember that.” The demagogue as the nation’s last best hope. Classic.

The centerpiece of the Trump campaign is now a “reality” TV story line, where validity is irrelevant, and outrageousness and shock are the only values. The story line is Trump as a victim under vicious assault by a vast conspiracy: “They will attack you, they will slander you, they will seek to destroy your career and your family, they will seek to destroy everything about you, including your reputation. They will lie, lie, lie, and then again they will do worse than that, they will do whatever is necessary.” And of course, the demagogue as martyr for the people: “Nevertheless, I take all of these slings and arrows gladly for you.” At the same time, he remains a winner: “The new, highly respected Rasmussen poll just came out this morning. Just released. Shows up nationally 2 points ahead, Trump. Beautiful.” And the climactic argument: “Vote for Donald Trump. You're going to see something and you'll be so happy. You'll be so thrilled.” Well, in that case . . .

So, as he says, Mr. Trump is now finally free to pursue politics “the way I want to.”

Last week USA Today called Mr. Trump a “dangerous demagogue.” Earlier in the week, the editorial board of the Los Angeles Times in its endorsement called him “a thin-skinned demagogue.” Dozens of other editorial boards and commentators have used the “D-word.” But what exactly does it mean?

Demagoguery is a problem implicit in democracy, an occasional illness, if you will, to which democracies are particularly prone. Democracy gives power to the demos, or people, and from time to time the people fall prey to the illusions peddled by a strongman who manipulates them emotionally with the goal of transcending ordinary political conventions or constitutional limits. We call such a person a “demagogue.” Hamilton warned in TheFederalist against leaders who begin “paying an obsequious court to the people; commencing demagogues, and ending tyrants.”

The demagogue label is thus highly elastic. The critical question is how to distinguish between a charismatic populist politician and a dangerous demagogue. What is that line and when is it crossed? Among political scientists and historians, there seems to be a consensus that when a politician exhibits each of the following six characteristic behaviors, he or she has crossed the line and can be considered a demagogue:

Inflammatory language. The speech of the demagogue is designed to excite popular passions and foreclose reasoned discussion; as Michael Singer, who wrote a recent study of the demagogue, put it, “bringing maximal heat and minimal light to the public discourse.”

Lots of heat, but little light, is an apt description of the Trump stump speech, and certainly fits what we heard coming from the Trump side of the stage at the first debate. The New York Times analyzed all 95,000 words uttered by Trump during one week, and concluded: “The most striking hallmark was Mr. Trump’s constant repetition of divisive phrases, harsh words and violent imagery.”

Exploitation of popular prejudice and false belief. The demagogue appeals to the darker side of human nature, targeting the lowest common denominator in a culture, especially fear, resentment, anger, and hatred for a group of “others.”

Washington Post columnist Michael Gerson argues, “Cynically exploiting fear is an art. And Trump is a Rembrandt of demagoguery.” Trump’s message is aimed at the darkest corners of the American psyche. By dismissing mutual respect and human dignity as only so much “political correctness,” he brought forth an eruption of latent anger, prejudice, hate, and misogyny, and rode this foul wave to the nomination.

Intolerance of criticism. The demagogue lashes out against every slight. Rarely content with simply disagreeing with opponents, he seeks to undermine their legitimacy. The demagogue seeks to silence or eliminate critics.

And so we see with Trump, whose “birther” libel was irresistible for its potential to de-legitimize President Obama, who wants to change the libel laws in order to silence his media critics, and who could not resist using a presidential debate to pursue a long-standing feud with another celebrity. In the same analysis of a week’s worth of Trump talk, the Times reported: “Mr. Trump tends to attack a person rather than an idea or a situation, like calling political opponents ‘stupid’ (at least 30 times), ‘horrible’ (14 times), ‘weak’ (13 times) . . . .”

Incitement to, or tolerance of, violence. Even before he embraces actual organized violence, the demagogue typically “green lights” violent acts by his supporters, and titillates his audiences by hints of violence to come.

Trump signaled his approval of violence at his rallies (“maybe he should have been roughed up” (about a protester assaulted by Trump supporters), “I’d like to punch him in the face”). His speeches are infused with words “kill,” “destroy” and “fight.” At an event in Raleigh, Mr. Trump was asked by a 12-year-old girl, “I’m scared — what are you going to do to protect this country?” His reply: “You know what, darling? You’re not going to be scared anymore. They’re going to be scared.”

Rejection of normal rules of political conduct. The demagogue thrills his supporters by bucking the norms of political life. He lies with impudence, validates previously off-limits calumnies against the targeted “other,” and declines to follow rules and procedures, accusing the established order of being corrupt.

Here Trump provides a textbook model, with a wholly unconventional campaign that violates every prior standard of acceptable political behavior, and repeated accusations that the process is corrupt and “rigged” against him.

Belief that the passions of the people justify violation of the constitution and laws. Demagogues typically do not understand or accept that in a constitutional democracy, the will of the people is limited by the rule of law.

It doesn’t matter how many people support closing mosques or registering Muslims, it violates the constitution and cannot be done. But Mr. Trump insists that it be done, and justifies it as the will of the people as embodied by him. When challenged that our troops might well refuse to obey an illegal order to kill the families of ISIS fighters, Trump replied: “They won’t refuse. They’re not going to refuse me. Believe me. . . . If I say do it, they’re going to do it.”

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The rise of a modern American demagogue has been expected for a long time. In 1997 the late philosopher Richard Rorty predicted that eventually “something will crack. The . . . electorate will decide that the system has failed and start looking around for a strongman to vote for . . . One thing that is very likely to happen is that the gains made in the past forty years by black and brown Americans, and by homosexuals, will be wiped out. Jocular contempt for women will come back into fashion . . . All the resentment which badly educated Americans feel about having their manners dictated to them by college graduates will find an outlet.”

As so many thoughtful commentators have noted, many of Trump’s most ardent supporters share some genuine grievances and anxieties. And in many ways the system has failed them, and failed us all. But the embrace of a demagogue, no matter how valid the popular resentments that fuel him, always ends badly. Always. At some point, even his most die-hard supporters will realize, as Mark Singer put it, “they’ve been sold out by a huckster who coveted their votes only for the sake of his colossal self-regard. And that, all along, he had nothing real to offer.”